Meat grinders or choppers which rotate at relatively low speeds, e.g., about 150 to 250 r.p.m., are used for the preparation of hamburger meat and other products. The meat supplied to the grinder is accompanied by bone particles and other hard particles, such as gristle, which are referred to herein collectively as "bone particles." Perforated plates constructed for collecting the bone particles separately from the meat are disclosed in U.S Pat. No. 3,934,827, U.S. Pat. No. 4,004,742 and my prior U.S. application Ser. No. 328,902, filed Dec. 9, 1981, now abandoned. The former patent also discloses structure for discharging bone particles from the grinder as they are collected.
The structure of U.S. Pat. No. 4,004,742 includes a perforated plate and a stud having a shaft portion journalled in a cylindrical bore in the plate. A counterbore adjacent to the upstream face of the plate and surrounding the cylindrical bore forms an annular bone-collecting pocket around the shaft portion. The bone particles are retained in the grinder as they are collected, and the collected particles are emptied periodically. The structure of the latter patent is capable of producing ground meat which is very low in bone particles, and only a small amount of meat is lost with the bone particles which are removed separately.
The structure disclosed in my aforementioned application Ser. No. 328,902 constitutes an improvement on the structure disclosed in my U.S. Pat. No. 4,004,742 wherein the discharge of the bone particles is accomplished in the application with but a slight change in the structure disclosed in my U.S. Pat. No. 4,004,742. In particular, the shaft portion of the stud is provided with a recess extending continuously therealong between the upstream and downstream faces of the perforated plate for discharging from the grinder the bone particles which collect in the pocket around the shaft portion.
The combination of the perforated plate and the grooved stud provided by the structure of the aforementioned application, now abandoned, may be employed in all domestic meat grinders having die plates of from 5 to more than 16 inches in diameter and a shaft of at least 1/2 inch in diameter. Because of this arrangement, opening the machine periodically to remove bone particles and the accompanying down time are substantially obviated and no parts additional to those previously employed are required in such medium and large size meat grinders.
While the foregoing arrangement has been used successfully in removing bone chips in meat grinding machines which have relatively large diameter cutting plates and hence, large diameter shafts which will accommodate the necessary peripheral groove, it has been found that in smaller size grinding machines, the shafts are not of sufficient diameter to permit the formation of a large enough longtitudinal peripheral groove in order to allow the passage of bone chips. Moreover, forming the peripheral grooves in the shafts, particularly when made in helical form, involves relatively expensive machining operations and, depending upon the shape of the peripheral groove, it can experience excessive wear which necessitates replacement of the shaft and/or the die plate from time to time.